This invention relates generally to a sootblower device for directing a fluid spray against a heat exchanger surface, and particularly, to such a device for providing improvements in the uniformity of the cleaning effect provided.
Cleaning highly heated surfaces, such as the heat exchange surfaces of a boiler, furnace, or the like, has commonly been performed by devices generally known as sootblowers. Sootblowers typically employ water, steam, air, or a combination thereof, as a blowing medium which is directed through one or more nozzles against encrustations of slag, ash, scale and/or other fouling materials which become deposited on the heat exchange surfaces.
Typical sootblowers of the long retracting type have a retractable lance tube which is periodically advanced into and withdrawn from the boiler and is simultaneously rotated such that one or more blowing medium nozzles at the end of the lance tube project jets tracing helical paths.
Operators of large-scale boilers are continuously striving to improve the efficiency of their operation. The fluid medium discharge by sootblowers constitutes a thermal efficiency penalty for the overall operation of the boiler system. In addition, sootblowers further require substantial quantities of superheated steam or other pressurized fluid in order to effectively operate. Therefore, operators of such devices attempt to minimize the frequency of operation of sootblowers and the quantity of fluid which they discharge during a cleaning cycle.
Most efficient cleaning operation occurs when the jet of fluid emitted from the nozzle progresses along the heat exchanger surfaces at a nearly uniform progression rate. Achieving such uniformity is difficult in situations where the distance between the sootblower nozzle and the surface being cleaned changes during the motion of the lance tube. For example, if the lance tube is rotated as it is extended and retracted from the boiler and the surfaces being cleaned are planar surfaces such as pendant wall sections of water tubes, operating the lance tube at a constant rotational speed produces significant variations in the progression rate of the cleaning medium stream as it traces its cleaning path on the surfaces. Thus, where the rate of jet progression is lowest, excessive quantities of sootblowing medium are used as compared with the amount required for effective cleaning. Moreover, physical deterioration of the heat exchanger surfaces may also occur where they are xe2x80x9cover cleanedxe2x80x9d in this manner. However, the cleaning requirements in areas where the jet progression rate is greatest may compel the operator to select rotation and translation speeds based on these xe2x80x9cworst casexe2x80x9d areas for those areas which further exacerbates the previously noted problems in the areas where jet progression is lowest.
In order to overcome the previously noted disadvantages inherent in sootblowers operating at constant rotational speeds, designers of such systems have employed various solutions. One solution involves a complex drive system for the sootblower utilizing variable speed motor controllers coupled with sensors which detect lance tube longitudinal and rotational position. An example of such a mechanism is described in U.S. Pat. No. 5,337,438 which is commonly owned by the Assignee of this application and is hereby incorporated by reference. Although highly effective, these systems impose a significant cost penalty due to the requirements of employing the previously noted controller and drive system elements. Thus, such prior art systems have cost disadvantages which may preclude their application where their capabilities may be effectively utilized. In addition to the previously noted shortcomings, such sophisticated sootblower systems pose maintenance challenges in the hostile environment in which they are employed.
Another example of oscillating type sootblower systems are provided with reference to U.S. Pat. Nos. 4,177,539 and 4,351,082, both of which are commonly assigned with application and are also hereby incorporated by reference. In accordance with the Elting U.S. Pat. No. 4,177,539 discloses an oscillating mechanism using a so-called xe2x80x9cscotch yokexe2x80x9d mechanism. This system produces an oscillating angular output for the lance tube which could approach a sinusoidal angular speed variation. However, the mechanism required according to the Etling Patent is a complex mechanism requiring specialized components and modifications to existing sootblower carriage systems.
Accordingly there is a need in the art to provide a sootblower system which provides a more constant rate of jet progression without the disadvantages of sophisticated control systems as noted previously. In accordance with the present invention, a lance tube drive system is disclosed which provides a purely kinematic oscillation motion. In one embodiment, a gear reduction unit driven through a power takeoff point of the sootblower carriage is coupled through a linkage to the lance hub to provide an oscillating motion. Due to the kinematics of the drive system, this approach provides a non-uniform angular velocity which is more closely modeled as a sine wave velocity curve. This curve when coupled with the radial distance between the surface being cleaned and the lance tube nozzle can be related to provide constant or nearly constant jet progression along pendant wall sections or other planar surfaces being cleaned by the sootblower nozzle. In another embodiment, the power for the lance tube rotational drive does not come from a power take-off point of the carriage, rather power is supplied by a separate drive motor.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.